don't call CopyBeforeWrite when returning non-const interator if the string is empty -- avoids assert and is not needed anyway since the iterator is never valid

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@27539 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/string.cpp

@@ -407,6 +407,20 @@ bool wxStringBase::Alloc(size_t nLen)
   //else: we've already got enough
   return TRUE;
 }
+  
+wxStringBase::iterator wxStringBase::begin()
+{
+    if (length() > 0)
+        CopyBeforeWrite();
+    return m_pchData;
+}
+
+wxStringBase::iterator wxStringBase::end()
+{
+    if (length() > 0)
+        CopyBeforeWrite();
+    return m_pchData + length();
+}
 
 wxStringBase::iterator wxStringBase::erase(iterator it)
 {